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BRES2015-0387 Geotechnical Update• L . Sladdm Engineering 45090 Golf Center Parkway, Suite F, Indio, CA 92201 (760) 863-0713 Fax (760) 863-0847 6782 Stanton Avenue, Suite C, Buena Park, CA 90621 (714) 523-0952 Fax (714) 523-1369 450 Egan Avenue, Beaumont, CA 92223 (951) 845-7743 Fax (951) 845-8863 800 E. -Florida Avenue, Hemet, CA 92543 (951) 766-8777 Fax (951) 766-8778 August 3, 2015 Mr. & Mrs. Scott & Dana Turban Project: Proposed Custom Residence 53-459 Via Dona — Lot 42D The Hideaway La Quinta, California Subject: Geotechnical Update - Project No. 544-15185 15-08-321 Ref: Geotechnical Engineering Report prepared by Earth Systems Southwest (ESSW) dated September 22, 2000; File No. 07117-10, Report No. 00-09-772 Report of Testing and Observation During Rough Grading prepared by ESSW dated August 28, 2002; File No. 07117-11, Report No. 01-07-718 Report of Testing and Observation During Rough Grading prepared by Sladden Engineering dated October 12, 2003; Project No. 544-2199 Report No. 03-10-647 As requested, we have reviewed. the above referenced geotechnical reports as they relate to the design and construction of the proposed custom residence. The project site is located at 53-459 Via Dona within the Hideaway Golf Club development in the City of La Quinta, California. It is our understanding that the proposed residence will be a relatively lightweight wood -frame structure supported by conventional shallow spread footings and concrete slabs on grade. The subject lot was previously graded during the rough grading of the Hideaway project site and was subsequently regraded. The rough grading included over -excavation of the native surface soil along with the placement of engineered fill soil to construct the building pads. The regrading included processing the surface soil along with minor cuts and fills to construct the individual building pads to the current configurations. Some additional over -excavation was performed in areas where . the building envelopes were reconfigured. The most recent site grading is summarized in the referenced Report of Testing and Observations During Rough Grading prepared by Sladderi Engineering along with the compaction test results. The referenced reports include recommendations pertaining to the construction of residential structure foundations. Based upon our review of the referenced reports, it is our opinion that the structural values included in the referenced grading report prepared by Sladden Engineering remain applicable for the design, and conC�f�i�sed residential structure foundations. i�• . NOV 2 3 2015 CITY OF LA GIUINTA COMMUNITY DEVELOPMENT Sladden Engineering l ' y ��wi _ _ r ��r y IY✓: r.._t�..5ltw. August 3, 2015 -2- Project No. 544-15185 15-08-321 Because the lot has been previously rough graded, the remedial grading required at this time should be minimal provided that the building falls within the previously established building envelope. The building area should be cleared of surface vegetation, scarified and moisture conditioned prior to precise grading. The exposed surface should be compacted to a minimum of 90 percent relative compaction is attained prior to fill placement. Any fill material should be placed in thin lifts at near optimum moisture content and compacted to at least 90 percent relative compaction. The allowable bearing pressures recommended in the referenced grading report prepared by Sladden Engineering remain applicable. Conventional shallow spread footings should be bottomed into properly compacted fill material a minimum of 12 inches below lowest adjacent grade. Continuous footings should be at least 12 inches wide and isolated pad footings should be at least 2 feet wide. Continuous footings and isolated pad footings should be.designed utilizing allowable bearing pressures of 1500 psf and 2000 psf, respectively. Allowable increases of 300 psf for each additional 1 foot of width and 300 psf for each additional 6 inches of depth may be utilized if desired. The maximum allowable bearing pressure should be 3000 psf. The recommended allowable bearing pressures may be increased by one-third for wind and seismic loading. Lateral forces may be resisted by friction along ,the base of the foundations/slabs and passive resistance along the sides of the footings. A friction coefficient of 0.50 times the normal dead load forces is recommended for use in design. Passive resistance may be estimated using an equivalent fluid weight of 300 pcf. If used in combination with the passive resistance, the frictional resistance should be reduced by one third to 0.33 times the normal dead load forces. The bearing soil is non -expansive and falls within the "very low' expansion category in accordance with 2013 California Building Code (CBC) classification criteria. Slab thickness and reinforcement should be determined by the structural engineer. We recommend a minimum floor slab thickness of 4.0 inches and minimum reinforcement of #3 bars at 24 inches on center in both directions. All slab reinforcement should be supported on concrete chairs to ensure that reinforcement is placed at slab mid -height. Slabs with moisture sensitive surfaces should be underlain with a moisture vapor retarder consisting of a polyvinyl chloride membrane such as 10 -mil Visqueen, or equivalent. All laps within the membrane should be sealed and at least 2 inches of clean sand should be placed over the membrane to promote uniform curing of the concrete. To reduce the potential for punctures, the membrane should be placed on a, pad surface that has been graded smooth without any sharp protrusions. If a smooth surface can not be achieved by grading, consideration should be given to placing a 1 -inch thick leveling course of sand across the pad surface prior to placement of the membrane. Based on our field observations and understanding of local geologic conditions, the soil profile type judged applicable to this site is So, generally described as stiff soil. The following presents additional coefficients and factors relevant to seismic mitigation for new construction based upon the 2013 California Building Code (CBC). Sladden Engineering August 3, 2015 -3- Project No. 544-15185 15-08-321 The seismic design category for a structure may be determined in accordance with Section 1613 of the 2013 CBC or ASCE7. According to the 2013 CBC, Site Class D may be used to estimate design seismic loading for the proposed structures. The 2013 CBC Seismic Design Parameters are summarized below. Risk Category (Table 1.5-1): I/II/III Site Class (Table 1613.3.2): D Ss (Figure 1613.3.1): 1.500g S1 (Figure 1613.3.1): 0.676g Fa (Table 1613.3.3(1)): 1.0 Fv (Table 1613.5.3(2)):1.5 Sms (Equation 16-37 (Fa X Ss)): 1.500g Sm1 (Equation 16-38 (Fv X S1I): 1.015g SDs (Equation 16-39 (2/3 X Smsl): 1.000g SM (Equation 16-40 (2/3 X Sm1I): 0.676g Seismic Design Category: D In addition, we have sampled the surface soil on the subject lots to determine the soluble sulfate content as it relates to selecting appropriate concrete mix designs. Testing indicates that the site soil is generally considered non- corrosive with respect to concrete. The testing indicated soluble sulfate content of 20 ppm (0.002 percent) that corresponds with the "negligible" exposure category in accordance with ACI 318-08, Table 3. Based upon this, the use of sulfate resistance concrete mixes should not be required. , If you have questions regarding this letter or the referenced reports, please contact the undersigned. Respectfully submitted, SLADDEN ENGINEERING Brett L. Anders BRETT L. Principal Engineer ci ALOE 5 i G No. C45389 n UA SER/gvm \ Exp. 9/30/16 r CIVIL =+ ENGINEERING 9F CAL Copies: 4 / Addressee Sladden Engineering Please verify that soils reports contain all of the above information. In addition, to assure continuity between the Investigation/reporting stage and the execution stage, please use the following checklist to verify that the conclusions and recommendations in the report cover all the required elements. Only then can we be assured that the construction documents address all of the site soil conditions. La Quinta Geotechnical Report Checklist Does the "Conclusions and Recommendations" section of the report address each of the following criteria? "Address"means: (a) the criterion Is considered significant and mitigation measure(s) noted, or; (b) the criterion is considered insignificant and explicitly so stated: Y s . No Criterion ❑ Foundation criteria based upon bearing capacity of natural or compacted soil. ❑ Foundation criteria to mitigate the effects of expansive soils. ❑ Foundation criteria based upon bearing capacity. of natural or compacted soil. ❑ Foundation criteria to mitigate.the effects of liquefaction. ❑ Foundation criteria to mitigate the effects of seismically induced differential settlement. ❑ Foundation criteria to mitigate the effects of long-term differential settlement. ❑ Foundation criteria to mitigate the effects of varying soil strength. ❑ Foundation criteria to mitigate'expected total and differential settlement. Any "No" answers to the .above checklist should be noted as specific required corrections. Sladden Engineering 6782 Stanton Ave., Suite A, Buena Park, CA 90621 (714) 523-0952 Fax (714) 523-1369 45090 Golf Center Pkwy, Suite F, Indio, CA 92201 (760) 863-0713 Fax (760) 863-0847 450 Egan Avenue, Beaumont, CA 92223 (951) 845-7743 Fax (951) 845-8863 Date: August 6, 2015 Account No.: 544-15185 Customer: Mr. & Mrs. Scott & Dana Turban Location: The Hideaway, 53-459 Via Dona, La Quinta Sulfate Series Analytical Report Soluble Sulfates per CA 417 . ppm 20 Soluble .Chloride per CA 422 IDIOM Sulfate 544-15185 080615 'TABLE 19-A-2—REQUIREME.RTS FOR SPECIAL EXPOSURE CO.NDIT OWS _ �1INIMUMI�, NORMAL'-WEIGM AND MAXIMUM • • WATER•tEMENTTT)OUS . UGHYy/OGHT. MATERIALS;• RAT)d; BY.: ' AGGREGA7ECORCAEiE :;::psl.•; .WEIGHT; NORFAAL''•WEIGHT• x 0.0M9.1or MPs EXPOSURE CONDITION AGGREGATE CONCRETE Concrete intended to have low permeability when AGGREGATE exposed to water 0.50 4,000 Concrete exposed to'freezing and thawing in a moist Mscdmum'Water- condition or to deicing chemicals 0.45 4,500 For corrosion protection for reinforced concrete Cament(Uous hUterlala:! Ratio; by:. exposed to chlorides from deicing Chemicals, salts or SULFATE �SOil IH SOIL, brackish water, orsprayfrom these'sources 0.40 5,000 TABLE 19-A-3—REQUIREMENTS. FOR CONCRETE EXPOSED TO SULFIATE-CONTAINING=SOLUTIONS - IA lower water-cancnddous materials ratio orhigher strength may bcrcquired for fow permeability•or forprotcetion against corrosion*of embedded items or freezing and thawing (Table 19-A-2)- 7Seawatec- . • .. ?Poaalan that has been determined by test or service record to improve sulfate resistanco when used in concrete eon- taitiing Type V ccmenL 2-264 UCHT.WEIGHT NORMAL -WEIGHT :AGGREGATE AGGREGATE CONCRETE Mscdmum'Water- f^,Horma6 We-Ight•and WATER- SOLUBLE Cament(Uous hUterlala:! Ratio; by:. ..Whtwelght ' SULFATE �SOil IH SOIL, WeN hQ.� H&mal- e:i ht• ' -Aooftnte Conaetb,•,P&1J SULFATE P R AGE BY SULFATE(SOa)•IN Aggregate x GbM9't0rMP1L EXPOSURE WEIGHT WATER, ppm CEMENT TYPE Concrete[ Negligible 0.00-0.10 0-150 Modcratc2, 0.10-0.20 150-1,500 II, IP(MS), LS OSO 4,000 (MS) Severe 0.20-2A0 1,50040,000 V 0.45 4,500 Very severe. Over 2.00 Over 10,000 V plus 6.45 4,500 pozzolan3 IA lower water-cancnddous materials ratio orhigher strength may bcrcquired for fow permeability•or forprotcetion against corrosion*of embedded items or freezing and thawing (Table 19-A-2)- 7Seawatec- . • .. ?Poaalan that has been determined by test or service record to improve sulfate resistanco when used in concrete eon- taitiing Type V ccmenL 2-264